Pattern matching in file and then display 10 lines above every time

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# 8  
Old 01-30-2008
not tested for performance
awk '
    print a[NR-i]
   for ( j=1;j<=NR-10;j++){
    delete a[j]
' "file"

# 9  
Old 01-30-2008
Hi, KevinADC.
Originally Posted by KevinADC
The English module is known to create inefficiencies in perl programs. See the English man page for details: English -

I am not sure if it affects the code you posted drl but you may want to take a look.
I looked over the reference, and added the sequence qw( -no_match_vars ) to my template. The warning is about a degradation in RE matching specifically. I added it to the short code I posted and it didn't seem to make a noticeable difference in a quick test (2 lines matched from the US Constitution from about 1000 lines). On the other hand, it's an easy thing to add.

Thanks for making me aware of that. Damian Conway does mention that in Perl Best Practices, but I haven't implemented all of that yet ... cheers, drl
# 10  
Old 01-31-2008

This one maybe ok for you,just try!

nawk '{
if (index($0,"pattern")!=0)
for (i=NR-10;i<=NR;i++)
print line[i]
}' filename

# 11  
Old 01-31-2008
Another suggestion...

Just give it a try and see.
for x in `grep -n "pattern" <filename> |cut -d":" -f1`
head -$x <filename> | tail -10

Its working but performance issue may be there.
# 12  
Old 01-31-2008
I think perl would be good for this, it certainly should be easy. Tie::File is good for working with large files since it does not read them into memory, but it does alter the original file so you have to make sure to open the file in readonly mode. A preliminary script:

use strict;
use warnings;
use Tie::File;
use Fcntl 'O_RDONLY';

tie my @file, 'Tie::File', 'path/to/file', mode => O_RDONLY
    or die "Can't open path/to/file: $!";
foreach my $i (10 .. $#file) {
    if ($file[$i] =~ /pattern/) {
        print qq{"pattern" found on line },$i+1,"$/";
        print qq{previous ten lines:$/}; 
        print map{"$_$/"} @file[$i-10 .. $i-1], "----------------------------";

I am not sure how efficient/ineffiecient this is though.
# 13  
Old 01-31-2008
Originally Posted by Karthikeyan_113
Its working but performance issue may be there.
I can see that if there are more than 1000 results, it will call heads and tails on the file for more than 1000 times.
# 14  
Old 10-20-2008
Originally Posted by namishtiwari
It's telling illegal option -B;I am using HP-UX.
gnu grep has the -B option ( lines before ) and a -A option ( lines after ) as well. You may find this on your box as ggrep or something like that, otherwise you could certainly get the gnu grep out here somewhere:
Installing GCC: Binaries - GNU Project - Free Software Foundation (FSF)

hagar the horrible
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